Lighting has SO many variables, it drives me nuts. For example:
Originally Posted by johnblagg
....from all my reseach the 600 watt Mh is the most effecient light available for lumens produced per watt .
Metal halides do put out about 125 lumens per watt, second only to high pressure sodium bulbs at 140. Unfortunately, between the heat generation and the emitted spectrum, a lot of the benefit is lost - that is, not all of the lumens are in the wavelengths they need to be.
(I'll ignore the measurement units, showing only the relative levels.) A MH bulb, typically around 4000°K color temperature, for example, has (roughly) an energy intensity of 5 units in the blue end, and about 12.5 in the red end. A HO T5 bulb, on the other hand, with a 6400°K color temperature, puts out about 100 and 90, respectively. (Which may - to some extent - explain the purple coloration at lower foot-candles than full sun.)
Amazing as it seems to me, and HPS bulb - as bright as they may be - puts out essentially no light in the blue end and about 1000x less
in the red end than does that T5 bulb.